Harmonic crystal oscillator



April 20, 1954 J. F. LAI'DIG 2,676,258

HARMONIC CRYSTAL OSCILLATOR /N VEN TOE J. F LA/D/G BV April 20, 1954 J.F. LAlDlG HARMoNrc CRYSTAL oscILLAToR 2 Sheelzs-SheerI 2 Filed July 20.1949 /A/l/ENFOR By J. F. LA/D/G ATTORNEY Patented Apr. 20, 1954 UNITEDSTATES PATENT OFFICE HARMONIC CRYSTAL OSCILLATOR Application July 20,1949, Serial No. 105,741

This invention relates to crystal controlled oscillation generators, andparticularly to harmonic crystal type oscillators which may be utilizedfor producing high frequency currents controlled by a mechanicalharmonic or overtone mode frequency of one or more piezoelectric crystalbodies operating in a frequency spectrum which may be of the order of upto 50 megacycles or more per second.

vOne of the objects of this invention is to pro- Vide a harmonic crystaloscillator capable of producing oscillations at a mechanical harmonicmode frequency of one or more associated piezoelectric crystal bodies,Without interference from the fundamental or a lower mode frequency ofsuch crystal body or bodies.

Another object of this invention is to improve the frequency stabilityof harmonic crystal oscillators.

Another object of this invention is to provide low current drain on thepower supply source for harmonic crystal oscillators.

Another object of this invention is to reduce parasitic oscillations inharmonic crystal oscillators.

y Another object of this invention is to reduce the number of circuitcomponents in oscillators operating at mechanical harmonic modefrequencies of a pluralityof piezoelectric crystal elements.

' A particular object of this invention is to provide a circuitimpedance arrangement presenting a high impedance to the undesiredfundamental mode frequency or frequencies of the associatedpiezoelectric crystal elements and, at the same time, a low impedance tothe desired harmonic mode frequency or frequencies, such as the third,fifth or other mechanical harmonic mode frequency or frequenciesthereof.

Another particular object of this invention is to provide a harmoniccrystal oscillator circuit capable of operation over a Wider range ofharmonic mode frequencies corresponding to the several harmonic modefrequencies of a series or plurality of different frequency harmonicmode piezoelectric crystal bodies. v

In oscillatory piezoelectric crystal elements of the high frequencytype, it has beenr difficult heretofore to utilize in practical systemsthe higher order mechanical harmonics of crystal elements. In accordancewith this invention, such mechanical harmonics of crystal elements maybe made use of, and circuits provided Which enable the crystal elementsto oscillate efciently at high frequencies which may be values up t theorder of 50. or more megacycles per second.

17 Claims. (Cl. Z50-36) For precision control of the frequency of anoscillation generator, it is desirable to utilize a piezoelectriccrystal body because of its inheru ently high frequency stability, andwhere the frequency desired is higher than that which may be obtainedconveniently from the fundamental or lower natural frequency mode ofvibration of the piezoelectric body, one or more of the mechanicalharmonic or overtone mode frequencies thereof, which have a higherfrequency than the fundamental mode frequency, may be `utilized foraccurate frequency control purposes in a suitable circuit.

A piezoelectric crystal body, such as a, known thin AT-cut quartzcrystal plate or disc adapted to operate in thickness mode vibrations ofthe shear type, will exhibit mechanical, and also elec trical, resonanceat odd harmonics of its fundamental thickness mode frequency, andaccordingly may be excited'at any selected one of its mechanicalharmonic mode frequencies by means of a suitable circuit; and in thecase of the known AT-cut quartz crystal plate referred to, the harmonicmode frequency may be nearly an exact third, fth, seventh or other oddorder overtone of the fundamental mode frequency thereof and therebyprovide a stable harmonic 'crystal body oscillatingl on its harmonicmode frequency for direct and accurate. working frequency controlpurposes at a comparatively high crystal vibrator frequency which mayconveniently be a valueup to 50 megacycles per second, or a considerablyhigherv value.

It will be understood that the harmonic mode vibration of the crystalelement itself, rather than the fundamental mode frequency thereof,` isof particular interest in order to obtain a high frequency crystalcontrol of the circuit frequency. For this purpose, the mechanicalharmonic of the crystal element may be anv odd order'harmonic of thefundamentalshear mode thickness vibration in an AT-cut or BT-cut quartzcrystal element, for example. Accordingly; with such a suitable type ofharmonic crystal unit or units. the circuits provided in accordance withthis in vention make commercially available an upwardly extendedfrequency range of reliable crystal controlled operation.

In accordance with this invention, a harmonic crystal oscillator circuitis provided which may be controlled in frequency by the harmonic modefrequency of the associated harmonic crystal body, or of aplurality ofsuch crystal bodies working at selected spaced points over at desiredrange of harmonic modefrequencies; and in accordance with a. feature ofthis invention, ka

frequency discriminator means may be employed in the associated circuitto discriminate against the undesired fundamental mode frequency of theharmonic crystal body or bodies, and at the same time permit the circuitto oscillate only on the desired harmonic mode frequency of the crystalbody or bodies.

The oscillator circuit may include a suitable electronic tube such as apentode designed for high frequency use and having the usual cathode,control grid, screen grid, suppressor glid and anode or plateelectrodes, and provided with the usual power supply sources for heatingthe cathode heater and for supplying suitable positive potentials to thescreen grid and plate elec trodes of the oscillator tube. Associatedwith the oscillating electrodes of the oscillator tube, which may be thecathode, control grid and plate electrodes, a bridge circuit may beprovided one of whose elements is a suitable piezoelectric crystal unitso disposed that the bridge is balanced at all frequencies except theseries resonant frequencies of the crystal body and no plate-to-controlgrid feedback occurs except at those series resonant frequencies of thecrystal body.

In a particular embodiment, the harmonic crystal oscillator circuitprovided in accordance with this invention may comprise a groundedcathode single oscillator tube of the pentode type acting as a source ofhigh gain, a frequency determining bridge system which may be connectedin circuit with the plate, control grid and grounded cathode electrodesof the pentode type oscillator tube and which may comprise a tunablecircuit tuned approximately to the desired frequency of oscillationdisposed in two of the bridge arms and provided with a capacitancedivider having the tap therebetween connected with the grounded cathodeelectrode of the oscillator tube, a frequency controlling harmoniccrystal body disposed in another bridge arm and operating at its seriesresonance harmonic frequency, a neu tralizing or balancing capacitordisposed in the remaining bridge arm and connected in the controlgrid-to-plate circuit of the oscillator tube for neutralizing orbalancing the capacitance across the crystal body and the straycapacitance associated with the crystal holder, suitable means foreffectively attenuating the undesired fundamental mode frequency of thecrystal body or bodies while simultaneously transmitting the de'- siredharmonic mode frequency thereof, and an output circuit for taking olffrom the oscillator circuit the desired harmonic mode frequency orfrequencies.

One of the objectives in a high frequency harmonic crystal oscillator.as for example when it is to be used in mobile or other isolated applimcations, may be a need for a lower current drain i on the power supplysource used therewith. This objective may be attained by utilizing asingle vacuum tube for the source of gain. Also, another objective is toreduce the possibility of parasitic oscillations in the circuit and forthis purpose the use of the capacitance tap on the capacitance dividingcapacitors associated with the harmonic crystal oscillator tank circuitreduces the possibility of parasitic oscillations, since the oscillatortube capacitance and other stray capacitances are then paralleled mainlywith the tank capacitors referred to, rather than with parts of the tankcircuit inductance element.

Another point of interest noted is that, to prevent the circuit fromoscillating at frequencies other than a series resonant frequency of thepiezoelectric crystal body, the capacitance divider formed by thecapacitors from the grid electrode of the tube to the two ends of thetank circuit may divide the voltage in the same ratio as the capacitancedivider formed by the capacitors from the cathode electrode of the tubeto the two ends of the tank circuit. The -capacitance between the gridelectrode and the plate end of the tuned circuit comprises the controlgrid-to-plate capacitance plus the associated stray capacitance of theoscillator tube connections plus the neutralizing or balancingcapacitor. Inasmuch as the control grid-to-plate capacitance and theassociated stray capacitance of the oscillator tube connections aresmall compared to the required capacitance, a neutralizing cpacitancewhich is large relative to the stray capacitances is required to balancethe circuit. Thus, the effect of the oscillator tube on the oscillationfrequency is greatly decreased. Moreover, in the circuit here utilized.since the capacitance of the crystal unit as measured from ground to thecontrol grid side of the crystal unit does not tend to prevent thecircuit from oscillating, any suitable harmonic crystal may be utilizedthat has a reasonably low capacitance across the crystal itself.

Another point of advantage noted is that the cathode of the oscillatortube being grounded, the use of a tube of the pentode type is therebyfacilitated, and moreover the use of the pentode type of vacuum tuberesults in-an increase in the gain and also in an increase in the plateresistance for the oscillator tube, and also in a decrease in thecontrol grid-to-plate capacitance thereof and hence a decrease in itseffect upon the oscillator circuit frequency.

In order to prevent oscillation of the circuit as a grid-plateoscillator at the undesired fundamental mode frequency of thepiezoelectric crystal element, a small discriminator capacitor may beadded in circuit between the plate electrode of the oscillator tube andthe plate end of the tuned circuit. This discriminator capacitor isadapted to present a high impedance at the fundamental mode frequency ofthe piezoelectric crystal element thus decoupling the plate circuit ofthe oscillator tube from the tuned circuit at that frequency and therebypreventing circuit oscillations at that undesired fundamental modefrequency. At the same time, this discriminator capacitor is adapted topresent a much lower impedance at the higher harmonic mode operating orworking frequency of the piezoelectric crystal element thus coupling theplate circuit of the oscillator` tube to the tuned circuit at thatharmonic mode frequency and thereby transmitting and permitting circuitoscillations at that desired harmonic mode frequency. Such adiscriminator capacitor is especially convenient when the oscillatormust be capable of operating over a relatively wide range offrequencies, since the discriminator capacitor provides a substantialmargin of frequency discrimination between the desired harmonic and theundesired fundamental mode frequencies. The circuit may thereby be madeto operate over a somewhat wider range of desired harmonic modefrequencies by the use of the discriminator capacitor method referredto, than by the use of other simple expediente to prevent 'oscillationsat the undesired fundamental mode frequency.

In order to obtain a Wide tuning range. as for gezogene `of differentfrequencies are utilized to covera desired relatively narrow range offrequencies, the tank circuit of the oscillator need not be separatelytuned to each operating frequency and accordingly multifrequencyoperation of the oscillator may be provided'by utilizing a suitableselector type of switching arrangement'to switch any one of the severalharmonic crystals, one at a time, into or out of the yoscillatorcircuit. The

Vswitching arrangement may be of the known turret type, or may be aremotely-operated arrangement utilizing suitable relays. The switchesand crystals may be placed relatively close to the oscillator tube inorder to keep stray shunt capacitances in the circuit as low aspossible.

The desired harmonic mode frequency or frequencies may be taken off froman output circuit having one terminal connected with the groundedcathode electrode of the oscillator tube and havling the other terminalconnected at a suitable point, as with an adjustable tap on theinductance winding of the tuned tank circuit.

Should it be desired to obtain a still higher output frequency than maybe conveniently obtained directly from the oscillator circuit producingthe frequency corresponding to the harmonic mode frequency of thepiezoelectric body,

an odd or even order electrical overtone such as the second or thirdAorder electrical harmonic overtone of the crystal mechanical harmonicmode frequency may be taken from the oscillator by a suitable outputcircuit. In such an arrangement, a tuned circuit provided in the outputor plate circuit of the oscillator tube may be tuned to a frequency nfwhere n is a value 1, 2, 3, etc., and where f is the operating orVworking mechanical harmonic mode frequency of the piezoelectric crystalbody.

For a clearer understanding of the nature of this invention and theadditional advantages, features and objects thereof, reference is madeto the following description taken in connection with the accompanyingdrawing, in which like reference characters represent like or similarparts and in which: g

Fig. 1 is a circuit diagram illustrating schematically a bridge typeharmonic crystal oscillator apparatus in accordance with this invention;

Fig. 1A is a circuit diagram illustrating a modification of theoscillator circuit of Fig. 1, in which the neutralizing capacitor isplaced directly across the control grid and plate electrodes of theoscillator tube;

Fig. 2 is a circuit diagram illustrating particularly at the left sideof broken line yy, a series of different frequency harmonic modecrystals Vwhich may be used in the bridge arm of Figs. 1,

fication of the oscillator circuit of Fig. 1, in which anelectricalharmonic or overtone of the voperating'mechanical harmonic modefrequency of the crystal oscillator is taken from the output.

Referring tothe. drawing, Fig. 1 is a circuit diagram illustrating aharmonic crystal oscillator circuit comprising generally an amplifler orsource of high gain V1, a bridge circuit B, a tuned tank circuit T, andan output circuit at I2 and I3 for taking off the harmonic mode crystaloscillations as provided by any of a plurality of dierent frequencyharmonic mode crystals X1, X2, X3, etc.

As shown in Fig. 1, the amplifier source of gain V1 may be in the formof a single pentode type vacuum tube electronic gain device V1 having agrounded cathode electrode I connected to ground 2 and heated by asuitable cathode heater 3 which may be energized by a suitable batteryor other power supply source 4, an input or control grid electrode 5which may be connected through a suitable grid leak resistor Ref to thegrounded cathode electrode I, a screen grid electrode 6 which may beconnected through a suitable bypass capacitor C10 to the groundedcathode electrode I, a suppressor grid electrode 'I which may beconnected with the grounded cathode electrode I, and an anode or plateelectrode 8 which, together with the cathode and control grid electrodesI and 5 may constitute .the oscillation generating electrodes of thevacuum tube V1. As shown in Fig. 1, the anode electrode 8 may beenergized with a suitable positive potential, through a suitable radiofrequency choke coil La, by means of a suitable battery or other powersupply source Ill having its negative terminal connected to ground 2 andto the grounded cathode electrode I. Similarly, the screen electrode 6may be energized with a. suitable positive potential through a lterresistor RF connected with the positive terminal of the power supplysource I 0. While particular forms for energizing the vacuum tube V1have been illustrated, it will be understood that any suitable means maybe utilized.

As illustrated in the drawing, a frequency controlling bridge system B.may be connected with the grounded cathode electrode I, Ythe controlgrid electrode 5 and the plate or anode electrode 8 of the vacuum tubeV1. A tank circuit T com- `prisinga parallel connected inductancewinding L1, a variable capacitor C3 and voltage dividercapacitors C4 andC5 is tuned approximately to the desired oscillation frequency and isdisposed in relation to two adjacent arms of the bridge B. 'Ihe tapconnection Il between the voltage divider capacitors C4 and C5 may beconnected with the grounded cathode electrode I of the vacuum tube V1. Aseries resonant harmonic crystal body X1 or X2 or Xa, etc., may beindividually disposed in a third arm of the bridge B and may beconnected in circuit between the control grid electrode 5 of vacuum tubeV1 and one end of the tank circuit T as shown in the drawing. In thefourth arm of the bridge B, a neutralizing or balancing capacitor C2 maybe provided and connected between the control grid electrode 5 of thevacuum tube V1 and the plate end of the tank circuit at 9, in order toneutralize or balance out the stray capacitance C1 across the crystalbody X1 or X2 or X3, etc. Between the plate electrode 8 of the vacuumtube V1 and the plate end 9 of the tank circuit T, a discriminatorcapacitor C may be added. Output circuit oscillations corresponding tothe desired crystal harmonic mode A frequency may be taken from thecircuit at outputterminalsJZ and .I3, the terminal I2 being ;desired;for thecircuit oscillations. -suchharmonicATecut orfBTecut quartzcrystals,

amazes fconnectedvwith 1 the f-.grounded `cathode:electrode I.of'.thevacuumtube andtheterminar I3 .being connected throughfa'couplingcapacitor C11 toa: tapf I4 provided on theninductance winding.Lraof'the.tunabletankncircuit T; thev position of the 4tap I4 onthecoilLr beingladjustedforproper impedancecmatchzto the output circuit.

;.'I-hef.harmonic crystal :body X1, X2v cin-Zeh, fetc.,

'rmaytfbe rany suitable: piezoelectric harmoniczcrys `tal ybody adaptedtoroperate 'and `worlr ata me chanical harmonic mode overtone frequencylof sits:v fundamentals. mode frequency. fFor. this purpose .f a.thickness+shear .imode AT-cut Vor BT-cut`quartz:crystal'ielement1operating and working at iansoddt order.overtone mechanical .harmonic of its.; fundamental thickness inode 'ofmotion, may :be: conveniently utilized, andthe desired harmonic.imodefifrequency .thereof mayfbez. the third,.fifth, seventh, orotherroddcrder harmonic modefre- ,quencythereof :corresponding ,to thefrequency Examples of with Jnountings andholdersi therefor to form a.harmonic crystal unit, are f disclosed in United zstatesPatentsNo.2,218,200, issued October 15, 194(lto. Lack,.Willardzand Fair, andNo.,2,453,435,

lissued November, 1948 toHnHavstad; and in applicationsS-erialllNo.1,623,150,. filed October 18,

11945 :by .L. J. La. :Briar-now lPatent No. 2,485,482 'dated November'.l 19.49;" and VSerial No- 26,013, filed ,May;.10, 1948 by F.Caroselli,now Patent llo.

2,509,478,idatedfMayfSO,.1950. While the present invention isz.described .particularly in connection withsuch harmonic mode crystalswhich employ thickness mode vibrationszof the.v shear type,` it 'willbelunderstoodthat the 4harmonic crystal body X1, X2,1 or Xzmay:bei.;any..suitable type of har monic crystal z body Lwherezthe capacityC1 across Ithe crystal-itselfis preferably of reasonable low value.Since, .in this circuit arrangement 1 as kshown bytherdrawing, thecapacity of `the crystal unit-X1, as measuredfrom/the control grid side5 of the crystal unit X1 to ground 2, does not tend toprevent thecircuit from oscillating, thecrystal body "X1 lmay be any .suitableharmonic crystal body that has va` reasonably low capacitanceCi `'acrossthe' crystal 4body itself.

As 'illustrated in the 1 drawing, thel lharmonic crystal body.` X1,4Xalornzg,feto., operates at one -of its harmonic series'resonancefrequencies; and

'for `operation at this series resonance frequency f the harmoniccrystalnbodyX1,.Xz or X3, etc., vmay beconnected in one' armfofthebridge B kthereby unbalancingthe bridge Bat such series resonance Jfrequency and providing a feedbackpath between .the.plateelectrodei. andthe control grid elec- 'trode 5 ofthe vacuum tube V1, the circuit beingtraced ,as follows: from theplate electrode: 8 of the vacuum .tube V1,sequentially, `through the Vdiscriminator.capacitor C,' the tank circuit.'I, and the harmonic crystalbody. X1, X2, or Xaetc., to thecontrol'grid electrode 5 oit thevacuum tube V1.

As illustrated lin the.drawinga single oscillator `tube .V1 may. beutilized, with a' resultant reducftion in the magnitude of'current drainupon the associated power supply sources 4 and I0, al feature which isofrinterestxin portable or mobile or other isolated installations; wher-ealow current .drain `may be desired, or r required.

Also as illustratedin thedrawing, thecathode electrode 5 of the vacuum.tube V1 is vthere shown as :being grounded.- at `2 andbeingso grounded,

the use' of the. vacuum tubexV1 `inthe formera pentodeV1 isthereby'facilitated. Moreover, the

v.use of the lpentode-'Vi resultsy not only Ain: an .ini" creaserinithefganr and the: platef-resistancdforcthe :vacuum tube V1, :but also f-inafa rdecrease fin `r the value .of the, grdeplate "capacitance, fortherztube vV1 and hencer4 ai smallerseirectifrom .tube capacitance uponl`the i fdesiredfrequency value: of the 'oscillator zfcircuit,'.A'lsc, 1. the use of `the vcapacitance 'tap :.LC4 i anda C5 on vthe 1harmonic icrystal oscillator tankr circuit :Ti reduces f the:possibility ofizparasiticf oscillations, sincel the vacuum;` tube V1,and the.Y stray.'.capacitancefv associated', therewith, `is @therebyv:parallel :with 'the :capac- `itors C4 :and .Csand'notfwith'parts 'ofthe-tank .circuit inductanceh. Accordingly;- with 'the .use

of;such afgsingle vpentode V1f of relativelyfgsmallinterelectrodetcapacitance and havingsa grounded cathode electrode.Izconnectedv to a. tap I I `between the capacitance dividers LCr. and.C5, there.` is:` pro- Avided not ,onlyaresultantl sav-ing in theenumberof .tubes used,1but1also the magnitude and-.number lofundesiredresponseifrequencies maybe reduced,

and the possibilityof obtaining; oscillator operation `onotherthan thecorrect frequency is :re-

duced. 1

The `neutralizing r or balancing capacitor .C2 which, as shown vin'. the1 drawing, is connected in the circi'iitlbetween the'control grid.electrode 5 of the vacuum tube Vr and the .plate endl9 of he tankcircuit T,.n1ay.be .made .upito acapacitance `value.`v such .thatf thetotal 'capacitance' of capacitor C2 plus the 'gridato-'plateninterelectrode capacitance of. the vacuum tube-V11 plus theistraycapacitance'associatedutherewith bears the same ratio to the straycapacitance i. C1, acrossithe harmonic crystal `body, fas 4the 1capacitance of -capacitcr C5 'bears to.` the `capacitance ofcapacitorfCi. Thelstray capacitances in parallel IWith theneutralizing-` capacitor. C25 are. usually Aquite small so that areal`capacitor C2v can be added to balance the circuity even when Vthevoltagedividing capacitors C4 and C5 are chosennin` the ratio for optimumoscillation of the circuit. Thus, the impedance of the. tank` circuitL1, Cs, C1, 'C5 in vthe `platecircuit'il of the vacuum tube V1 may bekept relatively high and that linthe 'control grid circuit' 5 `thereofmay be kept'. relatively llow, thereby 4resulting in a #maximum strengthof oscillation-and.' a decreased. eliect of the tube `V1 `upon thedesiredv oscillator lfrequenz-:y

of a suitable impedance value :to attenuate or in effect block the.undesired lower frequency fundamental modebscillation and, at the sametime, transmit the 1 desired i higher frequency harmonic modeoscillation. Accordingly, .the

discriminatoncapacitor C 4may be designed to present arelativelyl highimpedance at .the undesired fundamental mode frequency =of the crystalbody `or b0di'esX1,X2 and X3, `and thus eiectivelyzrdecouple .the .plate`electrode 8V of. the oscillator' tube V1 `from l .the 4tuning circuit LL1, C3, C4 and C5 at such undesired.;l fundamental mode .frequency or t'frequencies ,ofA the crystal :bodies tX1, X2, ornXs. :rButf at .thedesired..` operating;` or Working f. frequency, 1 Vwhich:` is; ther;harmonic mode frequency of the. harmonic crystal body X1, X2, or X3, thediscriminator capacitor 4C is designed to present a much lower impedanceand thus effectively couple the plate electrode 8 of the oscillator tubeV1 to the tuning circuit L1, C3, C4 and C5 only at such desired harmonicmoder frequency or frequencies of the crystal bodies X1, X2, or X3.

While the discriminator capacitor C may be utilized to block or preventfundamental frequency mode and simultaneously permit harmonic frequencymode oscillation in connection with only a single crystal body X1, X2,or X3, such a discriminator capacitor C is also' particularlyadvantageous when utilized in connection with a series or plurality ofharmonic crystal bodies X1, X2 and X3 operated at spaced differentharmonic mode frequencies over a desired range of frequencies.Y Thus,where a wider range of harmonic mode operating frequencies, asprovidedby a series of ysuch harmonic modey crystal bodies X1, X2, and X3, maybe desired, or where the required range of such operating frequenciesmay put thev highest fundamental mode frequency of the series of crystalbodies X1, X2, and X1 so close to the lowest harmonic mode frequencythereof asv to preclude the use of other simple methods for maintainingadequate margins, then the method as here provided by the discriminatorcapacitor C may be utilized.

Accordingly, due to the method of using the capacitor C for preventingfundamental mode oscillations while simultaneously permitting harmonicmode oscillations, the circuit shown in the drawing utilizing aplurality of harmonic crystal bodiesvX1, X2, X3, etc., formultifrequency channel operation, may be made to operate over a somewhatwider range of working harmonic mode frequencies. The tank circuit T,comprising the parallel connected inductance winding L1 and capacitorsCs, C4, and Cs'may be tuned to suit the harmonic mode frequencies withinthe range of such frequencies; and in order to obtain a wider tuningrange, the tanlr circuit T may be tuned by adjustment of the variable ,1

L1 which may be set at the properpointl thereon for the purpose ofproperly matching the iinpedance of the output'circuit to the impedanceof the oscillator circuit. Y

1 It Will be noted that the oscillators shown in Figs. l and 1A areadapted to operate directly ,i

Vtuning of the oscillator tank circuit L1, C4, Cs, C3.

Fig. 3 shows an adaption of the circuit shown in Fig. l which may besimilarly applied to Fig. lA and used when a still higher outputfrequency is desired or required, than can be obtained directly from theharmonicmode frequencies `of the crystal X1 or `X2 or X3 etc. As shownin electrode 8 of vacuum tube V1 and the discriminator capacitor C. Theoutput of the desired electrical harmonic frequency may then be takenfrom the circuit by means of a small link coupling coil L4 as shown inFig. 3, or by other suitable means of couplings to the electricalharmonic tuned circuit H. It should be noted that the presence of tunedcircuit H in the plate circuit of the oscillator tube V1 does not affectthe operation at the crystal harmonic oscillation frequency due to thefact that the impedance of tuned circuit H at a submultiple -of itstuned electrical harmonic frequency will be very low.

While particular'forms of output circuits have been illustrated in Figs.1, 1A and 3, it will be understood that there are other ways in whichoutput'oscillations vmay be taken off and obtained. Fig. 2, as alreadyindicated, is a circuit diagram utilizing the same circuit as shown inFig. 1, but illustrating more particularly at the left side of brokenline y-y, the plurality of separate and different frequency harmonicmode crystals X1, X2, X3, etc., adapted to be selectively connected, oneat a time, into the associated arm of the bridge B of Figs. 1, 1A or 3,by means of suitable selective switches Y1, Y2, Y2, etc., respectively,which may be selectively operated by remotely controlled selectiverelays Z1, Z2, Z3, etc., respectively, thereby to providemulti-frequency oscillations in the oscillator circuit of Figs. l, 1A or3 at any one ofa series of desired crystal controlled frequenciesextending over a relatively narrow range of frequencies. It 'will benoted that, while'in' Fig.'2"the plurality of crystals is crystalarrangement shown inl Fig. 2 maybe applied equally well in the samemanner tothe circuits shown in Figs. 1A and 3, or to other circuitarrangements whichv may be used.

'As an illustrative example for va particular harmonic crystaloscillator circuit constructed in accordance with thecircuit of`Fig; 1Aas provided with crystals shown more particularly by Fig. 2, andutilizing 'six such individual A'I'Lcut harmonic mode crystals X1, X1,etc., operating separately at six different workingv thickness modemechanical (5th) `harmonic frequencies spaced at intervals over a rangeof frequencies of 4300Vkilocyclesl per second, which range may be placedanywhere within the range of frequencies extending from 25.7 to .39.7megacycles per second,r the vacuum tube .V1, may be aA pentode `vknownas the .403B or other suitable source of gain, thepowensup'ply source I0may be a battery of about Y voltsdirect-current potential orothersuitable source of powersupply, and the component circuitresistors,condensers, and in ductance windings thereof may have valuesapproximately as follows: inductance coil LF about microhenries,inductance winding L1 about 0.7 microhenry, capacitor C about vl0micromicroe farads, stray capacitance' C1 about l0 'micromicrofarads,capacitor C2 .about 1.5 micromicrofarads, capacitor C3 about 7-50micromicrofarads, capacitor C4 `about .75. micromicrofarads,

- capacitor Csabout 18 micromicrofarads,. capaclil itor Cio Y about500i. micromicroi'arads; `capacitor Cn aboutl vInicromicroiarads,fresistorv Rg nabout 100,000'ohms and resistor'RFfabout 1,000 ohms.

Although this invention hasbeen described and illustrated in relation-to specific arrangements,` it

it .to` be understood .that it'fisfcapableofiapplication in otherorganizations.A andis therefore snot to be .limited tothe particularembodiments disclosed.

What is claimedis:y

l. Harmonic crystal oscillator 4apparatus comprisingfanelectronic'gainsource'V having input and outputcircuits; means includinga bridgenetworbcoupling. said input circuit with said outputeircuit,saidicouplingmeans including a connectionV to said4 bridgenetworkforming. a commonreturn circuit;y for both" said input and output?circuits of saidzgainr source, said lbridge network' includingin one-part thereofv a seriesresonant harmonic mode frequency piezo-electriccrystal body whicheisfdisposedin; circuit A'between said. input? andlsaid `output i circuitseand said bridge network inclu-ding directly-vtherein as 1 an other..J and,A unitaryyf component parte thereof asingleituned` tank circuitwhich z` isf: disposed in circuit between saidcrystal-bodyancltsaid` `output circuit, said tuned circuit beings tuned`substantiallyyto said har-monicfzmode frequency of -said crystalbody,Aand. mreanscomprisingea:frequency discriminatorfcapacitorf disposedf incircuit be'- tween` said tunedlcircuiti and said.. gain 4.source outputcircuit andahavingL a capacitance value sunicienftrifor transmittingvoscilla-tionsfrom said output :circuit yto vsaid inpu-t'circuitlat saiddesired harmonic-anode.frequency` ot; said: crystalv body whilesimultaneously;A attenuatingeand blocking oscillations suilicientlya'ttthecundesired funda mental inode` ffrequencyfot: said-i. crystal.body to substantially destroysscillaticx'rl ofjsaidapparatus at :saidAundesired fundamental l:mode:frequency,

2;' .Harmonic crystals. oscillator/apparatus com prising :,a-n,lelectronica.;V ga-in ,souroechaving input and Youtput circuitsra abridge1 network.; coupling said,- input circuitwithzsaidz outputtcircuit; saidbridge network including` ameutralizingbapacitor disposed in one-.bridgeamr thereoffin .a circuit between said;y input .anelxsaidfzoutput-.circuits,said bridge Inetworlzr.includingya4 seriesfiresonantharmoniccmode fairequencyr-piezoelectric :crystal 4body disposed inanother :andi-adiacenti :crystal bridge armv thereof in circuit:betweernl said inputan'd said "output circuits and said-1 bridge:network ,ine cluding aftuned tank. circuitdisposedzacrossssaidl:ist-mentioned4 adiacentiV bridgef f arms fr and diss posed in i,circuit .betweenfsaid `crystal body and said output circuit,A saidtunedcircuitbeing;` tuned substantially. to said harmonic,modetfrequency ofsaidcrystal body, said tuned .circuitcomprising an.,inductor-. direcitli'p connected inparallel A with two. remainingseries-connectd` capacitance arms of saidbridge network, aconnection tothe junction" between said' last=mentioned series connected capacitance"arms f' comprising L means' forminga` common return'circuitiforboth saidinputf andi said"A output circuits oi" saidl gain' source,` and:meanscomprising') a'y frequencyf discriminator capacitor'disposedinvcircuiti'between said tuned circuitr and said `v output circuit! andhaving; f af capacitancev value isuili'cient for r trans#mittingoscillations from said outputcircuitv to said `input circuit at:said: desired harmonicfmod'e frequency of said :crystallbody whilelsimultanea ously"attenuatingi'andblocking'ioscillations suilifcientlyy:at fthe tundesired :,fundamentalxzmode' tfreel quency of" said1mcrystal bony?A tozrendensa-idf appa ratus-non-oscillatory at saidfundamental mode frequency. y

3;, Harmonic crystal oscillator apparatus comprising an electronic/gainsourcehavingan anode electrode; a control grid electrodeand a cathodeelectrode; a `bridgenetwork connected with :said anode, controlgridzfand cathode electrodes,A said bridge network having a pluralityof'loridge4 arms, a'series-resonant harmonic mode `frequency.piezoelectric crystal body'disposed in one of saiclbridge arms incircuit between said anode 1 and control grid electrodes,` and3impedance elements disposed respectively in the remaining of`saidrbridge arms, said remaining bridgearmsi comprising oneia-rmdisposed incircuit betweenisaidanode andi-'conrtrol grid electrodes andtwo'otherzadjacent 'bridge armshaving av grounded tap connectiontherebetween connecteddirectly withrsaidccathodefelectrode,ia tunedVtankcircuit including reactance means, connected directly.' in shuntacross; said last-'mentioned two: other "adj acentiiibri'dge arms, saidi tuned circuit" .being tuned i substantially i to saidharmonic modefrequency of saidcrystal body and connected in'v circuitl betweeny saidcrystal body and `said anode. electrode `of said gain source, anda4frequency discriminator capacitor disposed in circuit ibetweenisaidi.anode'electrode offsaid gain source andsaid tunedcircuia .thettcapacitance value of said discriminatorycapacitorfbeing of suiliciently highimpedanceffat'rther` undesired fundamental mode frequency ofsaidfcrystal. body to decouple said anode electrode fromfsald-tunedcircuit.' at' said fundamental! Inodel frequency thereby constitutingmeans for preventing circuit oscillations at saidfundamental;modeifrequency of said-'crystal body; and said`capatdtancevalue being simultaneously of sufliciently''low-imped' anceat said desired' operatingy harmonic mode frequency of "saidcrystal bodytofcouple-saidfane` ode electrode tor said'v tuned`vvl circuit -`at saidharmonic mode frequencyfthereb'y constituting-means for permittingcircuit'oscillations at -said harmonic overtone mode `frequency of'saidcrystal vbody.

4i.y Harmonic crystal oscillatorl apparatus -'comprising an electronic`gain 'source having'an anil, series-resonant harmonic modeY frequency:piezoelectric crystal bodydisposed in one1off'said`bridge arrnsand incircuit'between said'control grid elec; trode andsaid anode electrode,a'fcondenser rdis'- posed in another offsaidbridgearms and in circuitbetween said controlgrid electrode and said anode electrode,` capacitorsdisposedrespectively in twoA other adjacentV bridgearms havingA agrounded tap connection therebetween rconnected with said groundedcathodeelectrodei; af tuned i tank circuit comprising aiparallel-'connectediine ductor and'condenser` connecteddirectly-inyshunt across said last-mentioned' capacitors-'in-saidlaste` mentionedtwo other adjacent-bridge arms, said tuned circuit being tunedsuibstantiallyeto said harmonic mode frequency of"said"crystalv body;said tunedcircuit having opposite ends comprising a control gridV and"connected" in circuitwithf said control grid electrodethroughsaidcrystal body and'anv anode `end 'connected in circuitiwith said anodeelectrode, afrequency discriminatoi capacitor disposed in'circuitbetweenn said anode electrode and said anode end of'saidtuned circuit,lsaid discriminator-f' capacitor-having a capaci tance valuer sufficientto constitutev means for transmitting'- said harmonic:A Inode-frequencyof lf3 said crystal body while simultaneously attenuating and blockingthe undesired fundamental mode frequency thereof, and an output circuitfor said harmonic mode frequency comprising connections leading to saidcathode and said anode electrodes.

5. Apparatus in accordance with claim'4 wherein said discriminatorcapacitor is disposed outside of said bridge network.

6. Apparatus in accordance with claim 4 wherein said discriminatorcapacitor is disposed in said bridge network, and in said bridge armbetween said condenser therein and said anode end of said tuned circuit;

7. Apparatus in accordance with claim 4 wherein said gain source is asingle vacuum tube of the pentode type having cathode, anode, controlgrid, screen grid and suppressor grid electrodes.

. 8. Apparatus in accordance with claim 'Tiwherein said output circuitconnections include a tap connection on said inductor of said tunedcircuit.

9. Apparatus in accord ance with claim '7 wherein said output circuitconnections include tuned circuit means disposed in circuit between saidanode electrode and said discriminator capacitor for producing anelectrical harmonic overtone of said crystal harmonic mode frequency.

10. Apparatus in accordance with claim 7 wherein said crystal body isone of a plurality of harmonic mode frequency piezoelectric crystalbodies each having a desired different harmonic mode frequency spaced atintervals over a desired range of frequencies, and wherein means areprovided for selectively and individually disposing each of said crystalbodies in said crystal bridge arm of said bridge network.

11. Harmonic crystal oscillator apparatus comprising an electronic gainsource having input and output circuits, means including a four-armbridge network coupling said input circuit with said output circuit ofsaid gain source, said bridge network comprising three series-connectedcapacitance arms, a fourth arm including therein a series-resonantharmonic mode frequency piezoelectric crystal body and a tuning circuitwhich is tuned substantially to said harmonic Inode frequency of saidcrystal body and connected directly across two diagonally oppositejunctions of said four bridge arms, said gain source input circuit beingconnected directly across the other two diagonally opposite junctions ofsaid four bridge arms, said gain source output circuit havingconnections to a pair of connection points across one only of said threecapacitance arms that is contiguous to one end of said tuning circuit,one of said last-mentioned connections including therein between saidone end of said tuning circuit and said gain source output a frequencydiscriminator capacitor having a capacitance value sufficient fortransmitting oscillations from said output circuit to said input circuitat said desired harmonic mode frequency of said crystal body whilesimultaneously having a capacitance value sufficient for rendering saidcrystal oscillator apparatus substantially non-oscillatory at theundesired fundamental mode frequency of said crystal body.

12. Apparatus in accordance with claim l1 wherein said discriminatorcapacitor is disposed in another one of said three capacitance arms ltal body, an amplifying device having anode,

14 cathodev and control' electrodes, a `single tank circuit consistingof an inductor, two series-connected capacitors connected across the twoterminals of said inductor and an adjustable capacitor connected acrosssaid two terminals of said inductor and adjusted to tune said apparatussubstantially to said harmonic frequency, a circuit connecting saidcathode electrode to a junction point between said two seriesconnectedcapacitors, a circuit connecting said anode electrode to one of said twoterminals of said inductor, a circuit connecting said control electrodeto the other of said two terminals of said inductor and including inseries therein said harmonic frequency piezoelectric crystal body, aneutralizing capacitor connection disposed between said controlelectrode and said circuit connecting said anode electrode to said oneof said two terminals of vsaid inductor, and adapted to feed back tosaid control-electrode from said tank circuit sufficient energy tosubstantially neutralize energy fed through capacitance eifects acrosssaid crystal body to said control electrode from said other of said twoterminals of said inductor in said tank circuit, and a frequencydiscriminator capacitor located between said anode electrode and saidtank circuit in said circuit connecting said anode electrode to said oneof said two terminals of said inductor and having sunicient capacitivereactance value at the undesired fundamental frequency of said crystalbody to substantially destroy oscillation of said apparatus at saidfundamental frequency.

14. Apparatus in accordance with claim 13 wherein said discriminatorcapacitor is inserted between said anode electrode and said neutralizingcapacitor connection.

15. Apparatus in `accordance with claim 13 wherein said discriminatorcapacitor is inserted between said inductor andsaid neutralizingcapacitor connection.

16. Apparatus in accordance with claim 13 wherein said circuitconnecting said anode electrode to said inductor includes therein aresonant circuit tuned to a harmonic of said crystal harmonic frequency.

17. A harmonic crystal type oscillation generator comprising a singleelectronic discharge device having cathode, control grid, screen grid,suppressor grid and plate electrodes, said cathode electrode beinggrounded, a grid leak resistor connected in circuit between said controlgrid and grounded cathode electrodes, a by-pass capacitor connected incircuit between said screen grid and grounded cathode electrodes, meansfor supplying positive potentials respectively to said plate electrodethrough a choke coil and to said screen grid electrode through 'aresistor, a fourarm bridge connected with said plate, control grid andgrounded cathode electrodes, said bridge having a capacitor disposed ina first arm, a capacitor disposed in a second and adjacent arm, aharmonic piezoelectric crystal body disposed in a third arm adjacentsaid second arm and a pair of series connected capacitors disposed inance winding having the opposite ends thereof connected directly acrosssaid bridge circuit between a connection point intermediate said secondand third bridge arms and a connection point intermediate said first andfourth bridge arms for tuning said bridge circuit with respect to anovertone harmonic mode frequency of said crystai body, said inductancewinding having a tap connection provided thereon, a grounded connectionpoint disposed intermediate said rst and second bridge arms andconnected with said grounded cathode electrode, a connection pointdisposed intermediate said third and fourth bridge arms and connectedwith said control grid electrode, a connection point disposedintermediate said series connected capacitors insaid fourth bridge armand connected with said plate electrode, said capacitor disposed in saidfourth bridge arm and connected in circuit between said connection pointtherein leading to said plate electrode and said connection pointbetween `said Iirst and fourth bridge arms, having a predeterminedfrequency discriminator capacitance value, said value being ofsufficiently high Aimpedance at the fundamental mode frequency of saidcrystal body to decouple said plate electrode from said tuned circuit atsaid fundamental mode frequeney thereby constituting means forpreventing circuit oscillations at said fundamental mode frequency ofsaid crystal body, and said value being simultaneously of sufficientlylow impedance at said desired operating harmonic mode frequency of saidcrystal body to couple said plate electrode to said tuned circuit atsaid harmonic mode frequency thereby constituting means for permittingcircuit oscillations at said harmonic overtone mode frequency of saidcrystal body, and an output circuit for said harmonic frequencyoscillations comprising a connection with said grounded cathodeelectrode and a connection with said tap connection provided on saidinductance winding of said tuned circuit.

References Cited in the le 0f this patent UNITED STATES PATENTS NameDate

